Treatment of iron ores



(NH4 2 s04 SEPARATION AND I SO 'UTION- I WASH IRON ORE 1 PRODUCT.

jam. 1, 1957 E, B, MANCKE 2,776,207

TREATMENT OF IRON ORES Filed April 5, 1951 2 Sheds-Sheet 1 {RAW one] /g a Almnalmufl/ SW Process. PRERoAsT. (500'f0 //0o"F.)

1 (H250 orPass'ib REC ovs RY o F (mw SO4ROAST. '3 an? #15 5% uan n- 1 in F'- AND SULFATE.

oxlolzER A0050. LEACH.

SEPARATION OXIDATIO N AUTOCLAVE. WASH- SOLUTION.

W SEPARATION INSOLUBLE AND RESIDUE, WASH. (CAN BE women UPIN REFRACT. v ennazcunome (SoadsJ one.

EVAP RATION BASIC IRON SULFATE.

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NH4 OH LEACH.

INYENTOR ATTORN Y Jan. 1, 1957 Filed April 5. 1951 IRAW ORE.

PREROAS T. (500 0 I/Oo'fi) ACID LEACH.

E. B. MANCKE TREATMENT OF IRON OREJS 2 Sheets- Sheet 2 OXIDIZER ADDED.

SEPARATION.

OXIDATION OF SOLUTION.

AUTOCLAVE ACID RECOVERY. Mil

SEPARATION AND mso LU BLE RES! DU E (can as WORKED UP INTO R EFRACTORY GRADE comma: 0R2.)

ELFoSsibQPm-L WASH.

Sugar 0.12%

30 lids.

FU R NACE. T

IRON ORE PRODUCT.

INVENTOR IBM- stat s, mewha ar .i quant ie .ghr

United States Patent TREATMENT on IRON oR-ES d a B- Manck Be hl hem a; a si aq t Be h ehem Steel Company, a corporationofliennsylvauia Application April 5, 1951, Se1 ial No.'2 19,-363

8 Claims. (Cl. 7 59-1 -15 g neral v qntain niekehin quantities offfroin 'bigs'jtn 11.50

:p ercent and cob alhin quantities of rfro rnZO QS to 013:041 ,ieent, on a calcined basis. Chromiu m is usu ally B$ nt I tid -QR in quan i i ran in tram 1-591 1 c -11 ln r -n n aM va type o qt ntea pval obalt, and chromiurnbresehts .a dill";cult -sep aration Ilam. ,Theseparation of the niqkeh oobalt'and phrb item h z r i -e ie l rim a tentseaside" t er "c ta n-estee the mai ufa turep se bsns ,tions callffor extremely slow vamounts of; l ng ties s uch a hieke landfi l-r man? n t esi s? e eq gfi {h ,typefitis neeessarythat theoreas chargedgp thei b l -ast rfiir a m s h ve ake en 91 mm??? 991th .,Lhave found that ores of theslMayari tyge, Whensolut i ize w r su f t r n e.s atesfll fiwsuh eflll t y u je te t ana t cl v tre tmen s -be ais -I y e anim torspradu nn t lowi niQ .-qt eltanimat tmium- Th fiat solut onv may be .P H' -F aibl ;mean: .o x mple t e -ma b Y i henlea tlwit su u ic;a@ ;9 leache s tlyiyu v .iil ariea i Ano he m tho s Bu ane th b l rafrt ar nsul ioni tim et toas h -st wh anzmaai ,sulf ate followed by alwater or sulf ic agidde In withe me hod: s lu ilizat a lian nselubletfii a ,inose re .mos ,ofthes ilisaaa t ip rtys thatsta wgt t mam mu :be p ate ite th so uti n Witien 9 a r ate s y th ab ve-me tione .,s lu liaatte gae lig in such manner s o; tl 1at at 1ea,st 85 percent o f the iron, nickel and cobalt dissolves, then roughly one-third, or Sl-ightlymore; ,of'the total chromium .willsalso dissolve.

"Upon autoclav-ing a sulfate solution.containingeiron,

\ wnickel, cobalt aud chromiumtvalues under suitabl'eicondis rth eh miuml th med a t qla-t tl K511911011- wmiumsis i t eh xava entstat sa rg mr in r be produce ,..w .ch twi .cq taini 11 p0.-, .1

vi.mium.unle i ye l tthe a t q ave tesdssliit ltain nsch qm umtwhi i rted m nan y n, a

tains. If desu ecl, part ofthe solu onxin'ayf be returned te tate of basic iron s ulfiate, most of thenickel, cobalt'and ltzjhrty lrl' m remaining.in solution. After'the completion or theia ut oclave treatment, the basic iron sulfate oreeipitatefis separated from the remaining solution, preferably 2,776,207 Fet ei tl Je i: 19

"ice agii'tocla to secure hexavalent chromium in the feed st k. Asubstantial proportion'of hexavalent'ehrom'um fean be formedjin the feed solution by roasting the bre' in n prior to leaching. However, more complete oxidation h sit t d by d g t idi i e agent s ch as potassium permanganate to the sulfate solution prior to an p laving r, i s l ting the ore in air is not essential with either of al h ns m t d newer ne adv o o Qti sth r in ai i fdf ed ftqmthel act dzsettlingand filteringproperties areobt I v H r t v rp' ccede eaching Ano he a .a air roast' gtheore is that ore whichhasbeen oast din thi stunner is more reactive" ha1f1 na ural .Q ea i given leaching treatment, solubilities' are ,highejr' if thefore h abet i fi in he y yfi 5 2 Q F b n part al-an jet u i A. s: Thes ad ant c are evident not only with subsequent aciki'leaehmg', a owhsn an e srqast i ts pw by a sqlub, Zi s r oniunisulflateroastanda l e' ac i Onemethod by which an iron ore product, low in nickel and chromium, can be obtained 'from"a Mayari type of ore by my'in'venti'on Would'beto' give the'b'resn o r'ti diging ,rqastyat approximately 800 F. The oxidizing roas i ,followed .by a second roas in whish the interoasted ore is treated with ammonium sulfate at about 8Q0 until iron, fnick'el, "cnbanfan-a combining chr0- We in the form of sulfates. Ammonia gjas' is liberated in this second roast Iaiideolleeted' for use in theiyroeess at a later stage, as Will be expla edfiThe g elles flrnans nes and al m nu t lea e lw t te o I o 7 m lehy fil ation. The residue contains silica insoluble chromium coft'npou nds. This residuevmay be utiligedih refractbriesif red. 'ljhe leach; solution is then autoelavd at suitable inperat ure and for a time suffiicientfto produce aj precipib .fi tr' tibnl an h pr le che i h mmo iu jli d bxiti T ei mm i hy oxide use t i 1 1 1 tu re can bep'repared from the ammonia gas liberatedcluring the an mqnum sulfate roastingfoperation; The'hy- :dr o rideleach removes sultur tr n the b a sic iron sulfate in theform of ammonium sulfate, leaving an iron prod- The jbasic i r on sulfate normally contains-approximately l8 ercent sulfur, while atten-leaching with ammonium hydroxide, the sulfur in'the remaining iron 'oxide or it-odv ductwill be below 2 percent. .The ammonium "sulfate reand aluminum sulfates andlpart, possiblyjZO percent, of

the original iron. Either all orrpartnofthis solution may t awe fe th a eva y fth t al able-meta sto the ammonium sulfate roasting operation, or tothe 3 leaching step immediately following roasting. A further alternative lies in liberating sulfur oxide gases from the solution, and using the sulfur gases in the acid leach step, either directly as the gas, or after reforming sulfuric acid from them, if the acid leach is made part of the process.

While the method outlined above produces a satisfactory end product of iron ore low in nickel, cobalt and chromium, an optional method of performing the same may be preferred in some situations, dependent on equipment and handling factors. Instead of pre-roasting the ore to obtain hexavalent chromium in the leaching step, the sulfate leach solution is oxidized with a permanganate or other oxidizing compound prior to autoclaving. Either method of oxidizing the soluble chromium insures an iron ore end product low in chromium. Additionally, pre-roasting may be used in conjunction with further oxidation of the leach solution. It has been found that when treating ore with both an oxidizing pre-roast and a subsequent oxidizing step upon the ore in solution, more iron dissolves in the leaching step because the ore is more reactive, thus more of the iron tends to be precipitated in the autoclaving step, and less oxidizer is required for the reason that the pre-roasting step accomplishes part of the oxidation. In addition, settling and filtering properties of the precipitated iron are improved by the pre-roast.

In the accompanying flow chart, Fig. 1, there is illustrated diagrammatically the process hereinbefore described.

As one specific example wherein my invention may be performed, a Mayari type ore having the following general analysis:

is pre-roasted in air at 800 F. for four hours. The pre-roasted ore is then roasted with ammonium sulfate at 800 F. for four hours to solubilize iron, nickel, cobalt, part of the chromium, and manganese and aluminum. The thus roasted ore is then leached with an aqueous solution of sulfuric acid and the soluble metal values extracted. After separating the insoluble residue from the sulfate solution, the solution is subjected to an oxidizing treatment by the addition of potassium permanganate. The oxidized solution is then autoclaved for one hour at 400 F. during which about 80 percent of the iron, previously in solution will be precipitated in the form of basic iron sulfate. After separating the precipitate from the remaining autoclave solution and thoroughly washing, the precipitate is leached with ammonium hydroxide (formed from ammonia gas produced in the ammonium sulfate roasting step), and an iron oxide ore product remains which has a nickel content of less than 0.10 percent, and chromium in an amount less than 0.15 percent. A typical example of an ore product made by my method analyzed as follows:

Sulfur (S) 1.40 (dry basis).

Another mode of performing my invention would be to give the ore an oxidizing roast and then leach the roasted ore with strong sulfuric acid to solubilize iron, nickel, cobalt, most of the soluble chromium, and manganese and aluminum. After separating the insoluble residue from the solution formed during leaching, said solution is introduced into an autoclave, either with or without further oxidation of the solution prior to the autoclaving step. Whether or not further oxidation is required will be determined by the sufficiency of the oxidizing roast, and the amount of chromium which can be tolerated in the product. After autoclaving the solution under suitable conditions of time, temperature and pressure, the resultant slurry is withdrawn, and the precipitated basic iron sulfate is separated from the remaining solution. The solution at this point contains most of the nickel, cobalt, the leach soluble chromium, manganese and aluminum, along with about 20 percent of the soluble iron. To obtain an iron ore product comparable to that obtained when an ammonium sulfate roast is used, as described in the previous example, the basic iron sulfate may be roasted to drive off sulfur oxide gases and leave an iron oxide low in nickel, cobalt and chromium. The sulfur oxide gases (S02 and S03) may be returned to the leaching operation.

In the accompanying flow chart, Fig. 2, there is a diagrammatic illustration of a method of performing my invention by use of a strong sulfuric acid leach, with subsequent treatment for the recovery of an iron oxide ore product by roasting.

In a specific example of performing my invention according to the process outlined in the accompanying flow chart, Fig. 2, an ore sample, having the same general analysis as that given for the sample of the previous example, is roasted in air at 800 F. and then leached with 40 percent (weight) sulfuric acid to solubilize most of the iron, nickel, cobalt, manganese, aluminum and soluble chromium. Upon the completion of the leach, the insoluble residue containing silica and part of the chromium is separated from the solution. The solution is then oxidized with potassium permanganate to insure oxidation of chromium to the hexavalent state, after which the solution is introduced into an autoclave. The autoclaving 7 operation may be performed at a temperature of 400 F. for one hour. During autoclaving, about 80 percent of the original iron will be precipitated in the form of basic iron sulfate, the other metal values present remaining in solution except for incidental and unharmful amounts which form part of the iron precipitate. After separating the precipitate from the remaining autoclave solution and thoroughly washing, the basic iron sulfate is roasted to convert it to iron oxide, the sulfur gases produced being collected, regenerated to sulfuric acid, and returned to the sulfuric acid leaching step. Regeneration of the sulfur gases to sulfuric acid before use in leaching may not be necessary in every case, for the gases may be introduced directly into the leaching solution. A typical example of an iron oxide ore product, made by the method of the foregoing, had the following analysis:

Iron (Fe) 68.7% (calcined basis).

Nickel (Ni) 0.03% (calcined basis). Cobalt (Co) 0.0l% (calcined basis). Chromium (Cr) 0.11% (calcined basis). Manganese (Mn) (0.10% (calcined basis). Alumina (A1203) 0.82% (calcined basis). Silica (SiOz) 1.00% (calcined basis).

In the example just given, the air roast at 800 F., prior to acid leaching, so conditions the ore that a. considerable quantity of the dissolved chromium will be in the hexavalent state after leaching. Depending on the ultimate use of the resultant ore product, further oxidation of the chromium may be unnecessary. However, when an ore product is desired having the lowest possible amount of chromium, it is necessary to oxidize the solution containing the metal values prior to autoclaving.

In performing my invention, the method to be used toisol'ubjiliie'rthe hie tal values and toreniove sulfatjeradicle {four the basic iron siilfate will depend primar y on operating considerations and on the type of solar i-Zing medium preferred in any individual. case. The resultant iidn ore product will be of thesame general character and quantity'in either of the proposed. methods shown in the flow charts. It is desirable, however, in order to fully realize on the economic possibilities of the; invention, that, whichever method of sulfation is used, the s'ul fating material be recovered. As has been shown in the example iii-which an ammonium sulfate roast is used, ammonia gas recovered from the roasting operation is used to form ammonium hydroxide for leaching the: precipitflted basic iron sulfate. The ammonium sulfate formed in the reaction which accompanies leaching of the basic iron sulfate is returned to the. ammonium sulfate roasting step. In this manner a closedcircu'it is maintained in respect to both the ammonia (NH4) and the, sulfate (S04) radicle, and by recycling the reformed ammonium sulfate to the ammonium sulfate; roasting step ino'stpf the sulfatitig material recovered, the original chai i f ammonium sulfate being constantly available for re-use in the treatment of fresh ore.

Likewise, when the means of sulfation is that of an air roast accompanied by a sulfuric acid leach, roasting of the precipitated basic iron sulfate to recover sulfur oxide gases, and eventually recycling the gases in the form of sulfuric acid to the leach, provides a means of recovery of sulfating material whereby only water and make-up reagent need be added to maintain the proper leaching conditions during subsequent treatment of fresh batches of ore. Here, again, it should be noted that regeneration of the sulfur gases to sulfuric acid before use in leaching may not be necessary in every case; the gases may be introduced directly into the leach solution, if desired.

I have found that while the autoclaving conditions given in each of the above examples give excellent separation of the iron from the non-ferrous metal values, the conditions are meant as examples only, for the temperature during autoclaving may be varied through quite a broad range, the practical temperature being in the vicinity of 390 to 420 F. At lower temperatures, e. g., 350 F., only a small part of the iron will precipitate, making the process impractical. Temperatures higher than 400 F. are effective but temperatures very much higher than 400 F., while effective to precipitate iron from solution offer some practical difiiculties because of the very high pressures which are then needed.

It should be pointed out that good nickel separations and quite good chromium separations can be made by the proposed methods even though care is not taken to assure the oxidation of the sulfate solution prior to autoclaving; however if an iron ore product very low in both nickel and chromium is desired, most of the chromium in the sulfate solution prior to autoclaving must be oxidized to the hexavalent state.

In the autoclave reaction, and in those which follow the autoclaving step, cobalt has been found to respond in a manner similar to that of nickel, therefore any remarks as to the action of nickel made herein will apply equally as well to cobalt.

I claim:

1. A method of treating nickeliferous, lateritic iron ore containing chromium to obtain an iron ore product low in nickel, cobalt and chromium Which comprises roasting the ore under oxidizing conditions at from be tween 500 to 1100 F., dissolving metal values of the ore by leaching the roasted ore with an aqueous liquid which contains a sulfur compound of the group consist- .ing of sulfuric acid, sulfur trioxide, sulfur dioxide and mixtures thereof, separating the solution formed during the leaching operation from the residue, oxidizing said separated solution to convert a substantial portion of the chromium to the hexavalent state, autoclaving said separated solution at a temperature of not less than about 390 F, to. prec p a as c ij oasuites; th t housi s t-f y SGPQI... is he slur y iq d'fi m' he ar ia a ad basic iron sulfate.

A m thQ of t eating a ick li ero ater tic r n r tainin ch om u to o in an o re PIOdJiQ 10W n ck l; cobalt d r m u wh ch c m s roasting the ore with-ammonium. sulfate, dissolving metal values of the ore by leaching. the roasted ore with. water, separating the solution formed during the leaching, op eration from the residue, oxidizing said separated "solution to convert a substantial portion of the soluble chr m um to thehexa i nt t auto lav n e osld zed solution at a temperature of not less than about 390 F. to precipitate basic iron sulfate thus producing a slurry, separating the slurry liquid from the precipitated basic iron sulfate. i

3. A method of treating a nickeliferous, lateritic iron ore containing chromium to obtain an iron ore product low in. nickel, .cobalt and vchromium which comprises roasting the ore with ammonium sulfate, dissolving metal values of the ,ore by leaching the roasted ore with an aqeuous solution containing sulfuric acid, separating the solution formed during the leaching operation from the residue, oxidizing said separated solution to convert a substantial portion of the soluble chromium to the hexavalent state, autoclaving the oxidized solution at a temperature of not less than about 390 F. to precipitate basic iron sulfate thus producing a slurry, separating the slurry liquid from the precipitated basic iron sulfate.

4. A method of treating a nickeliferous, lateritic iron ore containing chromuim to obtain an iron ore product low in nickel, cobalt and chromium which comprises pre-roasting the ore under oxidizing conditions at from between 500 to 1100 F., roasting the pre-roasted ore with ammonium sulfate, leaching the roasted ore with water, separating the solution formed during the leaching operation from the residue, oxidizing said separated solution to convert a substantial portion of the soluble chromium to the hexavalent state, autoclaving said separated solution at a temperature of not less than about 390 F. to precipitate basic iron sulfate thus producing a slurry, separating the slurry liquid from the precipitated basic iron sulfate.

5. A method of treating a solution containing iron and chromium sulfates which comprises oxidizing the solution to convert a substantial part of the chromium to the hexavalent state, autoclaving the oxidized solution at a temperature of not less than about 390 F. to precipitate an iron compound having an iron to chromium ratio considerably higher than the iron to chromium ratio of said solution.

6. A method of treating a nickeliferous lateritic iron ore containing chromium to obtain an iron ore product low in nickel and chromium, which comprises sulfating the chromium, nickel and iron and dissolving the sulfates to form an aqueous solution of such values, separating the solution from the residue, oxidizing said separated solution to convert a substantial portion of the chromium to the hexavalent state, autoclaving the solution at a temperature of not less than 390 F. to precipitate an iron compound, and separating the solution containing nickel and chromium from the precipitated iron compound.

7. A method of treating a nickeliferous lateritic iron ore containing chromium to obtain an iron ore product low in nickel and chromium, which comprises subjecting the ore to an oxidizing roast, sulfating the chromium, nickel and iron and dissolving the sulfates to form an aqeuous solution of such values, separating the solution from the residue, oxidizing said separated solution to convert a substantial portion of the chromium to the hexavalent state, autoclaving the solution at a temperature of not less than 390 F. to precipitate an iron compound and separating the solution containing nickel and chromium from the precipitated iron compound.

8. A-method of treating nickeliferous,- lateritic iron ore containing chromium to obtain an iron ore product low' in nickel, cobalt and chromium which comprises dissolving metal values of the ore by leaching with an aqueous liquid which contains a sulfur compound of the group consisting of sulfuric acid, sulfur trioxide, sulfur dioxide and mixtures thereof, separating the solution formed during the leaching operation from the residue, oxidizing said separated solution to convert a substantial portion of the soluble chromium to the hexavalent state, autoclaving said oxidized solution at a temperature of not less than about 390 F. to precipitate basic iron sulfate thus producing a slurry, and separating the slurry liquid from the precipitated basic iron sulfate.

References Cited in the file of this patent UNITED STATES PATENTS 981,451 McKechnie et al. Jan. 10, 1911 1,237,765 Eustis Aug. 21, 1917 1,258,934 Nitchie Mar. 12, 1918 1,364,573 Moore Jan. 4, 1921 8 Eustis Ian. 10, Caron Mar. 18, Davison Apr. 8, Read Apr. 27, Whetzel June 18, McBerty Nov. 2, Clark Sept. 22, Westby Sept. 5, Udy June 11, Udy Nov. 4, Foerster et al. Feb. 3, Poole et a1 Sept. 5, Hayward Feb. 5, Thomsen Feb. 23,

OTHER REFERENCES Standard Methods of Chemical Analysis, by Scott, 4th edition, vol. 1, pp. 249, 250. Pub. by D. Van Nostrand Co., Inc., New York, 1925.

A Comprehensive Treatise on Inorganic and Theoretical Chemistry, by Mellor, vol. 14, pub. by Longrnans, Green and Co., 1935, page 323. 

5. A METHOD OF TREATING A SOLUTION CONTAINING IRON AND CHROMIUM SULFATES WHICH COMPRISES OXIDIZING THE SOLUTION TO CONVERT A SUBSTANTIAL PART OF THE CHROMIUM TO THE HEXAVALENT STATE, AUTOCLAVING THE OXIDIZED SOLUTION AT A TEMPERATURE OF NOT LESS THAN ABOUT 390*F. TO PRECIPATE AN IRON COMPOUND HAVING AN IRON TO CHROMIUM RATIO CONSIDERABLY HIGHER THAN THE IRON TO CHROMIUM RATIO OF SAID SOLUTION. 